The invention is based on a priority application EP 05292232.5 which is hereby incorporated by reference.
The invention relates to a monitoring device for monitoring an array of electrical units, in particular an array of high capacity light emitting diodes (LEDs), connected in series and driven by a constant electric current.
The invention also relates to a signalling device, comprising an array of lighting units, in particular high capacity light emitting diodes (LEDs), connected in series, and a constant current source coupled to the array of lighting units for driving the lighting units.
Additionally, the invention relates to a use of the above-mentioned signalling device. For railway signalling purposes, conventional signalling lamps (e.g., 12 VAC, 35 W) are being replaced by arrays of high capacity light emitting diodes (LEDs; e.g., 4 V per diode, 350 mA current) in connection with special mirror/lens systems. A major advantage of using LEDs instead of conventional lamps resides in their superior durability which entails an increased cost-effectiveness of operation.
However, in particular when employing LED arrays of the above-mentioned type for signalling purposes, for instance in railway systems, some kind of electric circuitry has to be provided which allows an easy and reliable detection of a malfunction of the LED array, e.g. due to failure of individual LEDs because of short circuits and/or disconnection, while ensuring a continued operation of the LED array in case of only minor problems, e.g. failure of only one diode in an array of twelve.